Flexible plastic film

ABSTRACT

The present invention relates to a flexible plastic film, and more specifically to a flexible plastic film having excellent flexibility while exhibiting high hardness. According to the present invention, the flexible plastic film exhibits flexibility, bending property, high hardness, scratch resistance and high transparency, and hardly has a risk of damaging the film even in a state of being warped for a long period of time, and thereby can he usefully applied to flexible mobile devices, display devices, front face and display unit of various instrument panels, and the like.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application is a continuation application of Ser. No.15/744,691 filed on Jan. 12, 2018, which is a 35 U.S.C. 371 NationalPhase Entry Application from PCT/KR2016/008571, filed on Aug. 3, 2016,which claims the benefit of priority based on Korean Patent ApplicationNo. 10-2015-01.09699 filed on Aug. 3, 2015, Korean Patent ApplicationNo. 10-2015-0130564 filed on Sep. 15, 2.015, Korean Patent ApplicationNo. 10-2015-0160673 filed on Nov. 16, 2015, and Korean PatentApplication No, 10-2016-0098076 filed on Aug. 1, 2016 with the KoreanIntellectual Property Office, the disclosures of which are incorporatedherein by reference in their entirety.

BACKGROUND OF THE INVENTION (a) Field of the Invention

The present invention relates to a flexible plastic film. Morespecifically, the present invention relates to a flexible plastic filmhaving excellent flexibility while exhibiting high hardness.

(b) Description of the Related Art

Recently, with the development of mobile devices such as smartphones andtablet PCs, thinning and slimming of substrates for display arerequired. Glass or tempered glass is commonly used as a material havingexcellent mechanical properties on windows or front boards for displaysof mobile devices. However, the glass causes the weight increase of themobile devices due to its own weight, and has a problem of breakage dueto an external impact.

Therefore, plastic resin is being studied as a substitute for glass. Theplastic resin composition is lightweight but hardly has a risk ofcracking and thus are suitable for the trend of pursuing lighter mobiledevices. In particular, in order to implement a film having highhardness and abrasion resistance properties, a composition for coating ahard coating layer made of a plastic resin onto a support substrate hasbeen proposed.

As a method of improving the surface hardness of the hard coating layer,a method of increasing the thickness of the hard coating layer can beconsidered. In order to ensure the surface hardness enough to replacethe glass, it is necessary to implement a thickness of a certain hardcoating layer. However, as the thickness of the hard coating layer isincreased, the surface hardness may be increased but the occurrence ofwrinkles and curls are increased due to curing shrinkage of the hardcoating layer, and at the same time cracking and peeling of the coatlayer are likely to occur. Therefore, the practical application of thismethod is not easy.

Korean Patent Laid-Open Publication No. 2010-0041992 discloses a plasticfilm composition using a binder resin containing an ultraviolet-curablepolyurethane acrylate-based oligomer and eliminating monomers. However,the plastic film disclosed above has insufficient strength to replace aglass panel of a display with a pencil hardness of about 3H.

Meanwhile, a display in which a part of the display device is bent orflexibly warped for aesthetic and functional reasons has recently beenattracting attention, and this tendency is noticeable particularly inmobile devices such as smartphones and tablet PCs. However, since glassis not suitable for use as a cover plate for protecting such a flexibledisplay, it needs to he replaced with a plastic resin or the like.However, for that purpose, it is not easy to produce a thin film havingsufficient flexibility while exhibiting a glass 1 of high hardness.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a flexible plasticfilm having excellent flexibility and bending stability while exhibitinghigh hardness.

In order to achieve the above object, the present provides a flexibleplastic film comprising:

a support substrate; and an ultraviolet curable coating layer formed onat least one surface of the support substrate,

wherein the film exhibits a pencil hardness of 6 H or more under a loadof 750 g, and

when placing the film at an interval of 4 mm in the middle of the film,allowing the film to stand while both sides of the film being folded at90 degrees toward the bottom surface at room temperature, and thenspreading the film on a flat bottom surface, a height lifted from thebottom surface is 0.5 mm or less.

The flexible plastic film according to the present invention exhibitsflexibility, bending property, high hardness, scratch resistance andhigh transparency, and hardly has a risk of damaging the film even inrepetitive, continuous bending or long-time folding state. Therefore,the plastic film can be usefully applied to bendable, flexible, rollableor foldable mobile devices, display devices, front face and display unitof various instrument panels, and the like.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view schematically showing a method for performing a bendingstability test of a film according to one embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The flexible plastic film of the present invention comprises: a supportsubstrate; and an ultraviolet curable coating layer formed on at leastone surface of the support substrate, wherein the film exhibits a pencilhardness of 6 H or more under a load of 750 g, and when placing the filmat an interval of 4 mm in the middle of the film, allowing the film tostand while both sides of the film being folded at 90 degrees toward thebottom surface at room temperature, and then spreading the film on aflat bottom surface, a height lifted from the bottom surface is 0.5 mmor less.

In the present invention, the terms such as first, second, etc. are usedto describe various components, and the terms are used only for thepurpose of distinguishing one component from another component.

Moreover, the terminology used herein is for the purpose of describingexemplary embodiments only and is not intended to limit the presentinvention. The singular expression includes plural expressions unlessthe context clearly indicates otherwise. It will be understood that theterms such as “comprise,” “include,” “have,” etc. as used herein specifythe presence of stated features, integers, steps, components, orcombinations thereof but do not preclude the presence or addition of oneor more other features, integers, steps, components, and/or combinationsthereof.

As the present invention allows for various changes and numerousembodiments, particular embodiments will be illustrated and described indetail below. However, this is not intended to limit the presentinvention to particular modes of practice, and it is to be appreciatedthat all changes, equivalents, and substitutes that do not depart fromthe spirit and technical scope of the present invention are encompassedin the present invention.

The flexible plastic film of the present invention will be described inmore detail below.

The flexible plastic film according to an embodiment of the presentinvention comprises: a support substrate: and an ultraviolet curablecoating layer formed on at least one surface of the support substrate,wherein the film exhibits a pencil hardness of 6 H or more under a loadof 750 g, and when placing the film at an interval of 4 mm in the middleof the film, allowing the film to stand while both sides of the filmbeing folded at 90 degrees toward the bottom surface at roomtemperature, and then spreading the film on a flat bottom surface, aheight lifted from the bottom surface is 0.5 mm or less.

In the present invention, “flexible” means a state having flexibility tosuch an extent that cracks of 3 mm or more in length do not occur whenwound on a cylindrical mandrel with a diameter of 4 mm Therefore, theflexible plastic film of the present invention can be applied to a coverfilm of a bendable, flexible, rollable, or foldable display or the like.

In mobile devices such as smartphones and tablet PCs and displays suchas LCD, the form in which a part of the display device is bent orflexibly warped for aesthetic and functional reasons has recently beenattracting attention, and this tendency is noticeable particularly inmobile devices. However, since glass is not suitable for use as a coverplate for protecting such a flexible display, it needs to be replacedwith a plastic film including an ultraviolet curable or thermal curableresin or the like.

Among the cover plates made of a plastic resin, curved films forming aconstant curvature and having a fixed form, or films having flexibilityto the extent that can be bent by hand have been developed up to now,but it is inadequate to develop films having flexibility to such anextent that cracks do not occur even in repetitive bending or long-timefolding state. Thinner films are advantageous for achieving flexibilitybut are relatively disadvantageous in terms of surface hardness.Therefore, it is not easy to provide a film having high flexibility andhigh hardness at the same time.

The present invention provides a plastic resin film including anultraviolet curable coating layer which is implemented so as tosimultaneously satisfy the physical property balance between flexibilityand high hardness, and a flexible plastic film which exhibits highhardness and particularly hardly has a risk of damage of the film evenby repetitive bending or folding operation, and thus can be applied to abendable, flexible, rollable, or foldable mobile device, or a displaydevice.

That is, the flexible plastic film according to the present inventioncomprises: a support substrate; and an ultraviolet curable coating layerformed on at least one surface of the support substrate, wherein thefilm exhibits a pencil hardness of 6 H or more under a load of 750 g,and when placing the film at an interval of 4 mm in the middle of thefilm, allowing the film to stand while both sides of the film beingfolded at 90 degrees toward the bottom surface at room temperature, andthen spreading the film on a flat bottom surface, the film exhibits abending stability to such an extent that a height lifted from the bottomsurface is 0.5 mm or less.

FIG. 1 is a view schematically showing a method for measuring a bendingstability property of a flexible plastic film according to oneembodiment of the present invention.

Referring to FIG. 1, the film is placed so as to be horizontal with thebottom, and set so that the interval between the portions folded at amiddle portion of the film is 4 mm. The film is allowed to stand at roomtemperature for a certain period of time, for example about 12 to about72 hours, while both sides of the films being folded at 90 degreestoward the bottom surface. The film is spread on the flat bottom surfaceso that the folded portion goes downward. By the method of measuring thestability against bending after 1 hour, the stability against bendingcan be measured.

At this time, in order to maintain the distance between the foldingportions constant, for example, the film is placed so as to be incontact with a rod having a diameter (R) of 4 mm, the remaining portionof the film is fixed, and the processes of folding and spreading bothsides of the film around the rod can be performed. Further, the foldedportion is not particularly limited as long as it is the inside of thefilm, and for convenience of measurement, the central portion of thefilm may be folded so that the remaining portions of the film excludingthe folded portion are symmetrical.

In measuring such stability, the flexible plastic film of the presentinvention has a height lifted from the bottom surface of about 0.5 mm orless, or about 0.3 mm or less, or about 0.2 nun or less even after it isallowed to stand in a state of being folded for about 12 to about 72hours, and it can be restored substantially to the original flat state.

Therefore, even in actual application conditions such as folding,rolling or warping for a long period of time, the possibility ofoccurrence of cracks or deformation of the film such as lifting, or ofdistortion of the film at the warped or folded portion is extremely low,and thus the flexible plastic film can be suitably applied for a coverplate of a flexible display.

Further, the flexible plastic film of the present invention can have apenal hardness of 6 H or more or 7 H or more under a load of 750 g,

As mentioned above, thinning the thickness of the film is advantageousfor realizing flexibility, but the surface hardness becomes relativelylow. Therefore, it is not easy to provide a film having a high hardnesssimultaneously while having high flexibility. However, the flexibleplastic film of the present invention achieved the bending stability of12 hours or more the high hardness of 6H or more or 7H or more under aload of 750 g, by matching with the two conflicting physical properties.

That is, the present invention has been completed on the basis of that,when a plastic film has a structure including a support substrate and acoating layer formed on at least one surface of the support substrateand at the same time satisfies a pencil hardness of 6 H or more under aload of 750 g and physical properties that restore to the original flatstate even after maintaining a bending or folding state for apredetermined time, it can be practically applied to bendable, flexible,rollable or foldable mobile device, display device, etc.

The flexible plastic film of the present invention which simultaneouslysatisfies these bending stability and surface hardness can he obtainedby optimizing the support substrate and the ultraviolet curable coatinglayer (hereinafter, referred to as a coating layer) formed on thesupport substrate.

For example, in the flexible plastic film of the present invention, thesupport substrate on which the coating layer is formed is an opticaltransparent plastic resin having an elastic modulus of about 4 GPa ormore as measured according to ASTM D882 and a thickness in the range of20 to 200 μm so that it secures flexibility and hardness, and can beused without particularly limiting the method and material for producingthe support substrate such as a stretched film or a non-stretched film.

Among the conditions of the support substrate, the elastic modulus maybe about 4 GPa or more, or about 5 GPa or more, or about 5.5 GPa ormore, or about 6 GPa or more, and the upper limit value may be about 9GPa or less, or about 8 GPa or less, or about 7 GPa or less. If theelastic modulus is less than 4 GPa, sufficient hardness cannot beachieved, and if the elastic modulus exceeds 9 Gpa which is too high, itmay be difficult to form a film having flexibility.

The thickness of the support substrate (nay be about 20 μm or more, orabout 25 μm or more, or about 30 μm or more, and the upper limit valuethereof may be about 200 μm or less, or about 150 μm or less, or about100 or less, or about 60 μm or less. If the thickness of the supportsubstrate is less than 20 μm, there is a possibility that breakage orcurling occurs in the process of forming the coating layer, and it maybe difficult to achieve high hardness. On the other hand, if thethickness exceeds 200 μm, the flexibility deteriorates and it may bedifficult to form a flexible film.

From the viewpoint of ensuring the processibility for the flexible filmand achieving the physical property balance between the high hardnessand the flexibility as described above, a support substrate having anelastic modulus of 4 GPa or more and 9 GPa or less and a thickness inthe range of 20 to 200 μm can be used.

More specifically, according to one embodiment of the present invention,the support substrate satisfies the above-described elastic modulus andthickness range, and for example, it may be a film including polyimide(PI), polyimideamide, polyetherimide (PEI), polyethyleneterephtalate(PET), polyethylenenaphthalate (PEN), polyetheretherketone (PEEK),cyclic olefin polymer (COP), polyacrylate (PAC), polymethylmethacrylate(PMMA), triacetylcellulose (TAC), and the like. The above supportsubstrate may have a single layer or a multilayer structure including,if necessary, two or more substrates composed of the same as ordifferent substances, and is not particularly limited.

Alternatively, according to one embodiment of the present invention, thesupport substrate may be a substrate comprising polyimide (PI).

Further, according to one embodiment of the present invention, thethickness ratio between the support substrate and the coating layer maybe about 1:0.05 to about 1:1, or about 1:0.1 to about 1:0.8. When thethickness ratio between the support substrate and the coating layer iswithin the above range, a flexible plastic film exhibiting high hardnessand flexibility can he formed more easily.

The flexible plastic film of the present invention includes anultraviolet curable coating layer formed on at least one surface of thesupport substrate.

According to one embodiment of the present invention, the coating layermay be formed on both surfaces of the support substrate.

In the flexible plastic film of the present invention, the coating layercomprises a crosslinked copolymer of a 3- to 6-functional acrylate-basedbinder and a 7- to 20-functional urethane acrylate-based binder; andinorganic fine particles having a bimodal particle size distributionincluding a first inorganic fine particle group having d₅₀ of 20 to 35nm and a second inorganic fine particle group having d₅₀ of 40 to 130nm.

As used herein, the acrylate-based means not only acrylate but alsomethacrylate, or derivatives in which a substituents are introduced intoacrylate or methacrylate.

The 3- to 6-functional acrylate-based binder is cross-linked with the 7-to 20-functional urethane acrylate-based hinder to form a copolymer, andcan impart high hardness to the coating layer formed after curing.

More specifically, the 3- to 6-functional acrylate-based binder mayinclude trimethylolpropane triacrylate (TMPTA), trimethylolpropaneethoxytriacrylate (TMPEOTA), glycerin propoxylated triacrylate (GPTA),pentaerythritol tetraacrylate (PETA), dipentaerythritol hexaacrylate(DPHA), and the like. The above-mentioned 3- to 6-functionalacrylate-based binder may he used alone or in combination of differenttypes.

According to one embodiment of the present invention, the 3- to6-functional acrylate-based binder has a weight average molecular weight(Mw) ranging from about 200 to about 2,000 g/mol, or from about 200 toabout 1,000 g/mol, or about 200 to about 500 g/mol.

According to one embodiment of the present invention, the 3- to6-functional acrylate-based binder has an acrylate equivalent weightranging from about 50 to about 300 g/mol, or from about 50 to about 200g/mol, or from about 50 to about 150 g/mol.

When the weight average molecular weight and the acrylate equivalentweight of the 3- to 6-functional acrylate-based binder are respectivelywithin the above-mentioned ranges, a coating layer having more optimizedphysical properties can be formed.

The 7- to 20-functional urethane acrylate-based binder is cross-linkedwith the 3- to 6-functional acrylate-based binder to form a copolymer,and may impart high hardness, flexibility and impact resistance to thecoating layer formed after curing. The 7- to 20-functional urethaneacrylate-based binder may be used alone or in combination of differenttypes.

According to one embodiment of the present invention, the cross-linked.copolymer may be one in which the 3- to 6-functional acrylate-basedbinder and the 7- to 20-functional urethane acrylate-based binder arecross-linked in a ratio of about 1:9 to about 5:5, preferably 1:9 toabout 4:6, more preferably from about 1:9 to about 3.5:6.5. By includingthe cross-linked copolymer in which the 3- to 6-functionalacrylate-based binder and the 7- to 20-functional urethaneacrylate-based binder are cross-linked in the weight ratio describedabove, it can exhibit sufficient flexibility and at the same timeachieve high hardness and good physical properties.

According to one embodiment of the present invention, the 7- to20-functional urethane acrylate-based binder has a weight averagemolecular weight ranging from about 2,000 to about 8,000 g/mol., or fromabout 3,000 to about 6,000 g/mol, or from about 3,000 to about 5,000g/mol which may be preferable for the optimization of the physicalproperties of the coating layer.

According to an embodiment of the present invention, the 7- to20-functional urethane acrylate-based binder may have an acrylateequivalent weight ranging from about 200 to about 1,500 g/mol, or fromabout 200 to about 1,000 g/mol, or from about 300 to about 600 g/mol, orfrom about 300 to about 500 g/mol. If the acrylate equivalent weight ofthe 7- to 20-functional urethane acrylate-based hinder is too high, thehardness of the coating layer may be insufficient, and if the equivalentweight is low, the hardness may be improved but the flexibility may bedeteriorated. From the viewpoint of balance between high hardness andflexibility as described above, the above-mentioned equivalent weightrange is preferable, and about 300 to about 500 g/mol may be mostpreferable.

When the weight average molecular weight and the acrylate equivalentweight of the 7- to 20-functional urethane acrylate-based binder arerespectively within the ranges described above, coating layers havingmore optimized properties can be formed.

As the 7- to 20-functional urethane acrylate-based hinder contains inthe molecule at least 7 acrylate groups capable of performing acrosslinking polymerization by ultraviolet rays, it is advantageous forachieving high hardness of the coating layer. However, the higher thecross-linking density, it allows the curls to be easily generated andthe adhesive force with the substrate is lowered, and so it is notsuitable for forming a flexible film.

Meanwhile, the 7- to 20-functional urethane acrylate-based bindercontained in the coating layer of the present invention includes atleast 7 polyfunctional acrylate groups and at the same time has aurethane bond in the molecule, and thus is excellent in elasticity andflexibility. Accordingly, when it is cross-linked with a 3- to6-functional acrylate-based binder at an appropriate weight ratio toform a copolymer, it serves to impart sufficient flexibility togetherwith high hardness to the coating layer. The 7- to 20-functionalurethane acrylate-based binder may contain 2 to 20 urethane bonds in onemolecule.

As such, the coating layer according to one embodiment of the presentinvention includes a crosslinked copolymer in which the 3- to6-functional acrylate-based binder and the 7 to 20-functional urethaneacrylate-based binder are cross-linked to each other, thereby impartinghigh hardness and flexibility to the flexible plastic film. Inparticular, it has high stability against bending, rolling or folding,and thus it is possible to secure excellent flexibility and stability,which hardly has a risk of damaging the film even when repeatedly warpedor folded for a long time.

The coating layer according to one embodiment of the present inventioncomprises inorganic fine particles having a bimodal particle sizedistribution including a first inorganic fine particle group having d₅₀of 20 to 35 nm and a second inorganic fine particle group having d₅₀ of40 to 130 nm. As described above, the coating layer of the presentinvention uses the inorganic fine particles exhibiting a bimodalparticle size distribution including the first and second inorganic fineparticle groups each having a specific range of d₅₀, thereby improvingthe hardness and flexibility of the coating layer simultaneously whilemaintaining the flexible property.

In the specification of the present invention, when a cumulativeparticle size distribution corresponding to particle sizes was measuredusing a laser light diffraction method (measurement method: sizedistribution by number is determined by using dynamic laser scattering,a solvent in which inorganic fine particles are dispersed, refractiveindex, viscosity, and dielectric constant of the inorganic fineparticles, the equipment name: Malvern Zetasizer Nano-ZS 90), theparticle size at the 10% cumulative is set d₁₀, the particle size at the50% cumulative to d₅₀, and the particle size at the 90% cumulative tod₉₀. The particle size distribution by the laser light diffractionmethod can show substantially the same distribution as that measuredwith. SEM or TEM by diluting a dispersion liquid in which inorganic fineparticles are dispersed in a solvent, or measured by analyzing the crosssection of the coating layer containing the inorganic fine particles bySEM or TEM.

The first inorganic fine particle group having the small particle sizerange contributes to the improvement of the hardness, and the secondinorganic fine particle group having the larger particle size rangecontributes to the improvement of bending property and flexibility. Inthis way, as other inorganic fine particle groups having differentparticle size ranges are mixed and used in addition to the cross-linkedcopolymer described above, it is possible to provide a coating layer inwhich the physical properties of hardness and flexibility are improvedsimultaneously.

As the first and second inorganic fine particle groups, for example,silica fine particles, aluminum oxide particles, titanium oxideparticles, zinc oxide particles or the like may be each independentlyused.

According to one embodiment of the present invention, the d₅₀ of thefirst inorganic fine particle group may be 20 nm or more, or about 21 nmor more, 35 nm or less, 30 nm or less, or 25 nm or less, and the d₅₀ ofthe second inorganic fine particle group may be about 40 nm or more, orabout 42 nm or more, or about 45 nm or more, and 130 nm or less, or 125nm or less, or 120 nm or less.

According to one embodiment of the present invention, the firstinorganic fine particle group may have d₁₀ of 10 to 19 nm, d₅₀ of 20 to35 nm, and a d₉₀ of 25 to 40 nm. Further, the second inorganic fineparticle group may have d₁₀ of 25 to 110 nm, d₅₀ of 40 to 130 nm, andd₉₀ of 60 to 150 nm.

According to one embodiment of the present invention, the content of thefirst inorganic fine particle group may be about 5 parts by weight ormore, or about 10 parts by weight or more, or about 15 parts by weightor more, based on 100 parts by weight of the coating layer, in order tocontribute to an improvement in high hardness. The content of the firstinorganic fine particle group may be about 50 parts by weight or less,or about 45 parts by weight or less, or about 40 parts by weight orless, or about 35 parts by weight or less, in order to satisfy theflexibility. By including the first inorganic fine particle group withinthe weight range described above, it is possible to form a flexibleplastic film having excellent physical properties simultaneouslysatisfying both high hardness and flexibility.

Further, according to one embodiment of the present invention, thecontent of the second inorganic fine particle group may be about 5 partsby weight or more, or about 10 parts by weight or more, or 15 parts byweight or more, based on 100 parts by weight of the entire coatinglayer, in order to contribute to an improvement in high hardness, andmay be about 50 parts by weight or less, or about 45 parts by weight orless, or about 40 parts by weight or less, or about 35 parts by weightor less in order to satisfy flexibility. By including the secondinorganic fine particle group within the weight range described above,it is possible to form a flexible plastic film having excellent physicalproperties simultaneously satisfying both high hardness and flexibility.

According to one embodiment of the present invention, the total contentof the inorganic fine particles including the first and second inorganicfine particle groups may be about 25 parts by weight or more, or about30 parts by weight or more, or about 35 parts by weight or more, basedon 100 parts by weight of the entire coating layer, in order tocontribute to an improvement in high hardness, and may be about 50 partsby weight or less, or about 45 pails by weight or less, or about 40parts by weight or less in order to satisfy flexibility.

According to one embodiment of the present invention, the first andsecond inorganic fine particle groups may be the same or different andeach independently surface-modified with any one or more silane couplingagents selected from the group consisting of (meth)arylsilane,methacryloxysilane, vinylsiloxane, epoxysilane, and mercaptosilane.

Since the first and second inorganic fine particle groupssurface-modified with the silane coupling agent as described above canreact with the acrylate group of the hinder, the adhesion to thesubstrate is high, they can be uniformly dispersed in the coating layer,and the hardness can be improved without deteriorating the flexibilityof the coating layer, which are therefore more advantageous.

According to one embodiment of the present invention, the first andsecond inorganic fine particle groups may be present in the weight ratioof about 9:1 to about 3:7, or about 8:2 to about 4:6, or about 7:3 toabout 5:5. By including the first and second inorganic fine particlegroups within the weight ratio range described above, it is possible toform a flexible plastic film having excellent physical properties withenhanced high hardness and flexibility.

Meanwhile, the coating layer of the present invention may furtherinclude additives commonly used in the art, such as a surfactant, a UVabsorber, a UV stabilizer, an anti-yellowing agent, a leveling agent, anantifouling agent, a dye for improving the color value, etc., inaddition to the above-mentioned binder, inorganic fine particles,photoinitiator and organic solvent. Further, the content thereof is notparticularly limited as it can be variously adjusted within the rangethat does not deteriorate the physical properties of the coating layerof the present invention. However, they may be contained in an amount ofabout 0.01 to 10 parts by weight based on about 100 parts by weight ofthe coating layer.

According to an embodiment of the present invention, for example, thecoating layer may contain a surfactant as an additive, and thesurfactant may be a mono- or bi-functional fluorine-based acrylate, afluorine-based surfactant, or a silicon-based surfactant. In this case,the surfactant may be included in a form of being dispersed orcrosslinked in the crosslinked copolymer.

Further, the additive may include a UV absorber, a UV stabilizer, andexamples of the UV absorber include a benzophenone-based compound, abenzotriazole-based compound, a triazine-based compound and the like.Examples of the UV stabilizer include tetramethyl piperidine or thelike.

The coating layer according to one embodiment of the present inventionas described above may be formed by photo-curing a coating compositioncomprising a 3- to 6-functional acrylate-based binder, a 7- to20-functional urethane acrylate-based binder, photoinitiator, inorganicfine particles having a bimodal particle size distribution including afirst inorganic fine particle group having d₅₀ of 2.0 to 35 nm and asecond inorganic fine particle group having d₅₀ of 40 to 130 nm,additives, and an organic solvent.

Examples of the photoinitiator may include 1-hydroxy-cyclohexyl-phenylketone, 2-hydroxy-2-methyl-1-phenyl-1-propanone,2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone,methylbenzoylformate, α,α-dimethoxy-α-phenylacetophenone,2-benzoyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone,2-methyl-1-[4-(methylthio) phenyl]-2-(4-morpholinyl)-1-propanonediphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide, orbis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, and the like, but arenot limited thereto. In addition, examples of commercially availableproducts include Irgacure 184, Irgacure 500, Irgacure 651, Irgacure 369,Irgacure 907, Darocur 1173, Darocur MBF, Irgacure 819, Darocur TPO,Irgacure 907, Esacure KIP 100F, and the like. These photoinitiators canbe used alone or in combination of two or more.

Examples of the organic solvent include alcohol based solvents such asmethanol, ethanol, isopropyl alcohol and butanol; alkoxy alcohol basedsolvents such as 2-methoxyethanol, 2-ethoxyethanol and1-methoxy-2-propanol; ketone based solvents such as acetone, methylethyl ketone, methyl isobutyl ketone, methyl propyl ketone andcyclohexanone; ether based solvent such as propylene glycol monopropylether, propylene glycol monomethyl ether, ethylene glycol monoethylether, ethylene glycol monopropyl ether, ethylene glycol monobutylether, diethylene glycol monomethyl ether, diethyl glycol monoethylether, diethyl glycol monopropyl ether, diethyl glycol monobutyl etherand diethylene glycol-2-ethylhexyl ether; aromatic solvent such asbenzene, toluene and xylene, and the like. These may be used alone or incombination.

The content of the organic solvent is not particularly limited since itcan be variously adjusted within a range that does not deteriorate thephysical properties of the coating composition, but it can included sothat the weight ratio of the solid content: organic solvent is about30:70 to about 99:1 based on the solid content of the componentscontained in the coating composition. When the organic solvent is withinthe above range, it can have appropriate fluidity and coating property.

The coating composition may be each sequentially coated onto the frontand rear surfaces of the support substrate, or simultaneously coatedonto both surfaces of the support substrate.

According to one embodiment of the present invention, the coatingcomposition comprising the above-described components can be coated ontoboth surfaces of the support substrate and then photo-cured to form acoating layer, thereby obtaining the flexible plastic film of thepresent invention. Here, the method of coating the coating compositionis not particularly limited as long as it can be used in the technicalfield to which the present technology belongs, and for example, a barcoating method, a knife coating method, a roll coating method, a bladecoating method, a die coating method, a micro gravure coating method, acomma coating method, a slot die coating method, a lip coating method, asolution casting method, or the like can be used.

The coating layer may have a thickness of about 3 μm or more, forexample about 3 to about 20 μm, or about 3 to about 15 μm, or about 3 toabout 10 μm after being completely cured. According to the presentinvention, it is possible to provide a flexible plastic film having ahigh hardness when a coating layer having such a thickness is included.

According to one embodiment of the present invention, the flexibleplastic film may further include at least one selected from a layer, amembrane, a film or the like such as a plastic resin film, a cohesivefilm, a release film, a conductive film, a conductive layer, a liquidcrystal layer, a coating layer, a cured resin layer, a non-conductivefilm, a metal mesh layer or a patterned metal layer on the top surfaceof at least one coating layer or between the substrate film and thecoating layer. For example, an antistatic layer having conductivity isfirst formed on a support substrate, and then a coating layer is formedthereon to provide an anti-static function, or a low refractive indexlayer is introduced on the coating layer to implement a low reflectionfunction.

Further, the layer, membrane, film or the like may be in any form of asingle layer, a double layer, or a laminate type. The layer, membrane,film r the like may be formed by laminating a freestanding film with anadhesive, a cohesive film, or the like, or may be laminated on thecoating layer by a method such as coating, vapor deposition, sputtering,or the like, but the present invention is not limited thereto.

The flexible plastic film according to the present invention can beproduced, for example, by the following method.

According to one embodiment of the present invention, the flexibleplastic film can be formed by a two-step process of first coating andfirst photo-curing a first coating composition on one surface of asupport substrate, and then second coating and second photo-curing thecoating composition on the other surface, that is the back side of thesupport substrate. At this time, the first and second coatingcompositions are the same as the above-described coating composition,and each of them distinguishes the composition coated onto only onesurface and the back surface.

In the case of forming the coating layer by this method, in the secondphoto-curing step, ultraviolet ray irradiation is performed not on thesurface coated with the first coating composition but on the oppositesurface, and thereby curls which may be generated due to curingshrinkage in the first photo-curing step can be cancelled out inopposite directions to obtain a flat flexible plastic film. Therefore,no additional flattening process is required.

However, the present invention is not limited thereto, and the curlbalance can also be adjusted by forming the coating compositionsimultaneously on both surfaces of the support substrate and then curingthe coating composition.

The flexible plastic film of the present invention exhibits excellentflexibility, bending property, high hardness, scratch resistance, hightransparency, high durability and stability against bending, rolling orfolding and thus can be used as a cover film of a next generationdisplay having bendable, flexible, rollable or foldable properties, andthe like.

For example, the flexible plastic film of the present invention canexhibit flexibility to such an extent that cracks do not occur whenwound on a cylindrical mandrel with a diameter of 4 mm or 3 mm.

Further, the flexible plastic film of the present invention may have apencil hardness of 6H or more, or 7H or more, under a load of 750 g.

In addition, the flexible plastic film can generate 2 or less scratcheswhen steel wool #0000 is attached to a tip having a contact area of 2cm×2 cm with respect to a plastic film in a friction tester and then thesurface of the plastic film is reciprocated 400 times under a load of500 g.

Further, the flexible plastic film of the present invention may have alight transmittance of 88.0% or more, or 90.0% or more, and a haze of1.5% or less, 1.0% or less, or 0.5% or less.

The flexible plastic film of the present invention can be utilized invarious fields. For example, the flexible plastic film of the presentinvention can be used as a flat-shaped as well as a curved, bendable,flexible, rollable or foldable-shaped mobile communication terminal, atouch panel of a smartphone or a tablet PC, and cover substrate orelement substrate of various displays.

Hereinafter, the operation and effect of the invention will be describedin more detail by way of concrete examples. However, these examples aremerely presented for illustrative purposes only, and the scope of theinvention is not determined thereby.

EXAMPLES Example 1

30 g of trimethylolpropane triacrylate (TMPTA) (manufactured by Cytec,Mw=296 g/mol, acrylate group equivalent weight=99 g/mol) as atrifunctional acrylate-based binder, 40 g of MU9800 (manufactured byMiwon, Mw=3500 g/mol, acrylate group equivalent weight=389 g/mol) as a9-functional urethane acrylate-based binder, 30 g of MU9020(manufactured by Miwon, Mw=4500 g/mol, acrylate group equivalentweight=450 g/mol) as a 10-functional urethane acrylate-based binder, 1 gof Irgacure 184 (manufactured by Ciba) as a photoinitiator, and 15 g ofmethyl ethyl ketone (MEK) were mixed to prepare an acrylate solution.

60 g of a solution in which a silica particle S1(d₁₀=17 nm, d₅₀=22 nm,d₉₀=28 nm, surface-modified with methacrylate silane coupling agent) wasdispersed in n-BA 3 (normal butyl acetate) in an amount of 50% by weight(hereinafter, referred to as S1 dispersion solution), and 50 g of asolution in which a silica particle S2 (d₁₀=29 nm, d₅₀=51 nm, d₉₀=74 nm,surface-modified with an acrylate silane coupling agent) was dispersedin MEK in an amount of 30% by weight (hereinafter, referred to as S2dispersion solution) were mixed with the resulting acrylate solution toprepare a coating composition.

The coating composition was coated onto both surfaces of a polyimidesubstrate (size: 20 cm×30 cm, thickness: 35 μm) having an elasticmodulus value of 6.0 GPa as measured according to ASTM D882 by a barcoating method, and photo-cured with a metal halide lamp having awavelength of 290 to 320 nm to form a coating layer.

After the curing was completed, the thickness of the coating layerformed on both surfaces was 6 μm, respectively.

Example 2

The coating layer was formed in the same manner as in Example 1, exceptthat the S2 dispersion solution was used in an amount of 83.3 g of andno additional methyl ethyl ketone solvent was contained.

Example 3

The coating layer was formed in the same manner as in Example 1, exceptthat 25 g of methyl ethyl ketone was used, and 37.5 g of a solution inwhich a silica particle S3 (d₁₀=108 nm, d₅₀=119 nm, d₉₀=131 nm,surface-modified with an acrylate silane coupling agent) was dispersedin MEK in an amount of 40% by weight (hereinafter, referred to as S3dispersion solution) was mixed instead of 50 g of the 52 dispersionsolution to prepare a coating composition.

The subsequent steps were carried out in the same manner as in Example 1to form a coating layer.

Example 4

20 g of TMPTA (manufactured by Cytec, Mw=296 g/mol, acrylate groupequivalent weight=99 g/mol), 40 g of MU9800 (manufactured by Miwon,Mw=3500 g/mol, acrylate group equivalent weight=389 g/mol), 40 g ofMU9020 (manufactured by Miwon, Mw=4500 g/mol, acrylate group equivalentweight=450 g/mol), 1 g of Irgacure 184 (manufactured by Ciba) as aphotoinitiator and 12 g of methylethyl ketone (MEK) were mixed toprepare an acrylate solution.

60 g of the S1 dispersion solution and 75 g of the S3 dispersionsolution were mixed with the resulting acrylate solution to prepare acoating composition.

The subsequent steps were carried out in the same manner as in Example 1to form a coating layer.

Example 5

Except for using a polyimide substrate (size: 20 cm×30 cm, thickness: 35μm) having an elastic modulus value of 4.2 GPa as measured in accordancewith ASTM D 882, the other steps were carried out in the same manner asin Example 1 to form a coating layer.

Example 6

Except for using a polyimide substrate (size: 20 cm×30 cm, thickness: 35μm) having an elastic modulus value of 7.6 GPa as measured in accordancewith ASTM D 882, the other steps were carried out in the same manner asin Example 1 to form a coating layer.

Example 7

30 g of TMPTA ((manufactured by Cytec, Mw=296 g/mol, acrylate groupequivalent weight=99 g/mol), 30 g of MU9020 (manufactured by Miwon,Mw=4500 g/mol, acrylate group equivalent weight=450 g/mol), 40 g of SC2152 (manufactured by Miwon, Mw=20,000 g/mol, acrylate group equivalentweight=1,333 g/mol) as a 15-functional urethane acrylate-based hinder, 1g of Irgacure 184 (manufactured by Ciba) as a photoinitiator, and 42 gof methyl ethyl ketone (MEK) were mixed to prepare an acrylate solution.

60 g of the S1 dispersion solution and 83.3 g of the S2 dispersionsolution were mixed with the resulting acrylate solution to prepare acoating composition.

The subsequent steps were carried out in the same manner as in Example 1to form a coating layer.

Example 8

20 g of AZO particle dispersion CX-610M (manufactured by Nissan, solidcontent 60%), 10 g of dipentaerythritol pentaacrylate (DPHA), 0.5 g ofIrgacure 184 (manufactured by Ciba) as a photoinitiator and 100 g ofethanol were mixed to prepare an antistatic layer composition.

The antistatic layer composition was coated on one surface of thepolyimide substrate used in Example 1 and photo-cured to form anantistatic layer having a thickness of 1 μm and a surface resistance of10⁹Ω/sq.

The coating composition of Example 1 was coated onto the upper surfaceof the antistatic layer and the other surface of the substrate on whichthe antistatic layer was not formed, and photo-cured to form coatinglayers each having a thickness of 6 μm.

Example 9

First, a coating layer was formed on both surfaces of the polyimidesubstrate by the same process as in Example 1.

22 g of hollow silica dispersion Thrulya 4320 (manufactured by Catalysts& Chemicals Ltd., solid content 20%), 4 g of dipentaerythritolpentacrylate (DPHA), 0.5 g of photoinitiator Irgacure 184 (manufacturedby Ciba), a fluorine-containing compound RS907 (manufactured by DIC,solid content 30%) were mixed to prepare a low refractive index layercomposition.

The low refractive index layer composition was coated onto one surfaceof the coating layer and photo-cured to form a low refractive indexlayer having a thickness of 120 nm and an average reflectance of 2%.

Comparative Example 1

The coating layer was formed in the same manner as in Example 1, exceptthat methyl ethyl ketone was used in an amount of 55 g and a silicaparticle was not contained in the coating composition.

Comparative Example 2

The coating layer was formed in the same manner as in Example 1, exceptthat methyl ethyl ketone was used in an amount of 12 g and only asolution in which a silica particle S4 (d₁₀=12 nm, d₅₀=17 nm, d₉₀=21 nm,surface-modified with an acrylate silane coupling agent) was dispersedin MEK (hereinafter, referred to as S4 dispersion solution) was used inan amount of 112.5 g.

Comparative Example 3

The coating layer was formed in the same manner as in Example 1, exceptthat methyl ethyl ketone was used in an amount of 35 g and only a S1dispersion solution was contained in an amount of 110 g.

Comparative Example 4

The coating layer was formed in the same manner as in Example 1, exceptthat a S3 dispersion solution was used in an amount of 125 g, a S4dispersion solution in an amount of 25 g, and an additional methyl ethylketone solvent was not contained.

Comparative Example 5

Except for using a polyimide substrate (size: 20 cm×30 cm, thickness: 35μm) having an elastic modulus value of 3.1 GPa as measured in accordancewith ASTM D 882, the other steps were carried out in the same manner asin Example 1 to form a coating layer.

Comparative Example 6

Except for using a polyethylene terephthalate substrate (size: 20 cm×30cm, thickness: 250 μm) having an elastic modulus value of 4.2 GPa asmeasured in accordance with ASTM D 882, the other steps were carried outin the same manner as in Example 1 to form a coating layer.

Comparative Example 7

Except for using 70 g of PS610 (manufactured by Miwon, Mw=5,400 g/mol,acrylate group equivalent weight=900 g/mol) as a 6-functional polyesteracrylate-based hinder instead of MU9800 and MU9020 in ComparativeExample 3, the other steps were carried out in the same manner as inComparative Example 3 to form a coating layer.

The main components of the coating layers of Examples 1 to 7 andComparative Examples 1 to 7 are summarized Tables 1 and 2 below,respectively.

In Examples and Comparative Examples, the particle size distribution(d₁₀, d₅₀, d₉₀) of the inorganic fine particles was measured in thestate of a dispersed solution using Malvern Zetasizer Nano-ZS 90 todetermine a size distribution by number.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Example 7 Acrylatebased TMPTA 30 30 30 20 30 30 30 binder (unit: g)MU9800 40 40 40 40 40 40 — MU9020 30 30 30 40 30 30 30 SC2152 — — — — —— 40 Inorganic fine S1 30 30 30 30 30 30 30 particles* S2 15 25 — — 1515 25 (unit: g) S3 — — 15 30 — — — S4 — — — — — — — Substrate andThickness 35 μm 35 μm 35 μm 35 μm 35 μm 35 μm 35 μm coating layer ofsubstrate Elastic 6.0 GPa 6.0 GPa 6.0 GPa 6.0 GPa 4.2 GPa 7.6 GPa 6.0GPa modulus of substrate Thickness 6 μm 6 μm 6 μm 6 μm 6 μm 6 μm 6 μm ofcoating layer Total 47 μm 47 μm 47 μm 47 μm 47 μm 47 μm 47 μm thickness

TABLE 2 Comparative Comparative Comparative Comparative ComparativeComparative Comparative Example 1 Example 2 Example 3 Example 4 Example5 Example 6 Example 7 Acrylate TMPTA 30 30 30 30 30 30 30 based binderMU9800 40 40 40 40 40 40 — (unit: g) MU9020 30 30 30 30 30 30 — PS610 —— — — — — 70 Inorganic fine S1 — — 55 — 30 30 55 particles* S2 — — — —15 15 — (unit: g) S3 — — — 50 — — — S4 — 45 — 10 — — — Substrate andThickness 35 μm 35 μm 35 μm 35 μm 35 μm 250 μm 35 μm coating layer ofsubstrate Elastic 6.0 GPa 6.0 GPa 6.0 GPa 6.0 GPa 3.1 GPa 4.2 GPa 6.0GPa modulus of substrate Thickness 6 μm 6 μm 6 μm 6 μm 6 μm 6 μm 6 μm ofcoating layer Total 47 μm 47 μm 47 μm 47 μm 47 μm 262 μm 47 μm thickness

*In Table 1 and 2, the content of the inorganic fine particles isrepresented by the net weight of only the inorganic fine particles (S1to S4) excluding the solvent according to the weight percentage of theinorganic fine particles dispersed in the solvent.

EXPERIMENTAL EXAMPLE

<Measurement Method>

1) Pencil Hardness

The maximum hardness without scratches was confirmed after moving thepencil back and forth three times at an angle of 45 degrees under a loadof 750 g using a pencil hardness tester in accordance with standard JISK5400-5-4.

2) Transmittance and Haze

The transmittance and haze were measured using a spectrophotometer(apparatus name: COH-400).

3) Bending Test

Each film was interposed and wound between cylindrical mandrels ofvarious diameters and then the minimum diameter at which no cracksoccurred was measured.

4) Bending Stability Test

FIG. 1 is a view schematically showing a method for performing a bendingstability test of a film according to one embodiment of the presentinvention.

Each of the films of Examples and Comparative Examples was cut, butlaser cutting was performed into a size of 80×140 mm so as to minimizefine cracks at the edge portions.

The laser cut film was placed on the fixing device, set so that theinterval between the folded portions was 4 mm, and then allowed to standat room temperature for 24 hours while both sides of the film beingfolded at 90 degrees to the bottom of the film. The film was then peeledoff and the film was turned over so that the folded portion wentdownward. The L-shaped SUS structure was placed thereon and the film wasfixed. The 3D image of the film shape was measured with anoncontact-type surface roughness measuring instrument (PLUTO 681, DukinLtd., use of 605 nm laser, resolution 0.1 μm), and the maximum height ofthe height Z lifted from the bottom was measured as the bendingstability property.

In addition, in order to measure the recovery of the films, the films inwhich the bending stability properties were measured were allowed tostand at room temperature for 1 hour.

The folded portion of the film was downwardly turned over. The □-shapedSUS structure was placed thereon and the film was fixed. The 3D image ofthe film shape was measured with a noncontact-type surface roughnessmeasuring instrument (PLUTO 681, Dukin Co., Ltd., use of 605 nm laser,resolution 0.1 μm), and the maximum height of the height Z lifted fromthe bottom was measured and the change in the appearance of the foldedportion were visually observed.

If Z is 0.1 mm or less and appearance change such as traces of foldedparts is insufficient, it is shown as OK, and if Z exceeds 0.1 mm or alarge number of traces remain on the folded portions, it is shown as NG.

The measurement results of the physical properties are shown Tables 3and 4 below.

TABLE 3 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Example 7 Pencil hardness 7H 8H 7H 8H 6H 7H 6H Haze  0.4%  0.3%  0.4% 0.4%  0.4%  0.3%  0.4% Transmittance 91.9% 91.8% 92.0% 91.9% 91.9%92.1% 91.7% Bending test  4 mm  4 mm  4 mm  4 mm  3 mm  4 mm  3 mmBending stability 0.2 nm 0.2 nm 0.2 nm 0.2 nm 0.1 nm 0.2 nm 0.1 nmRecovery OK OK OK OK OK OK OK

TABLE 4 Comparative Comparative Comparative Comparative ComparativeComparative Comparative Example 1 Example 2 Example 3 Example 4 Example5 Example 6 Example 7 Pencil hardness 4H 5H 8H 5H 4H 6H 8H Haze  0.2% 0.3%  0.4%  0.4%  0.3%  0.5%  0.3% Transmittance 92.1% 91.9% 91.8%91.8% 92.1% 92.0% 92.0% Bending test  3 mm  4 mm 5 mm   4 mm   3 mm 20mm 8 mm Bending stability 0.1 nm 0.2 nm Unmeasurable 0.3 mm 0.1 mmUnmeasurable Unmeasurable Recovery OK OK NG OK OK NG NG

Referring to Tables 3 and 4, the films of the present inventionexhibited excellent characteristics in terms of each physical property,and particularly showed excellent stability in bending tests includinghigh hardness.

On the other hand, the films of Comparative Examples had lowered pencilhardness or did not exhibit sufficient bending durability to be suitablefor flexible films.

What is claimed is:
 1. A flexible plastic film comprising: a supportsubstrate; and an ultraviolet curable coating layer formed on at leastone surface of the support substrate, wherein the thickness ratiobetween the support substrate and the coating layer is 1:0.05 to 1:1,wherein the film exhibits a pencil hardness of 6 H or more under a loadof 750 g, and when placing the film at an interval of 4 mm in the middleof the film, allowing the film to stand while both sides of the filmbeing folded at 90 degrees toward the bottom surface at roomtemperature, and then spreading the film on a flat bottom surface, aheight lifted from the bottom surface is 0.5 mm or less.
 2. The flexibleplastic film according to claim 1, wherein of the support substrate hasan elastic modulus of 4 to 9 GPa as measured according to ASTM D882, 3.The flexible plastic film according to claim 1, wherein the supportsubstrate has a thickness of 20 to 200 μm.
 4. The flexible plastic filmaccording to claim 1, wherein the ultraviolet curable coating layer hasa thickness of 3 to 20 μm.
 5. The flexible plastic film according toclaim 1, wherein ultraviolet curable coating layer includes acrosslinked copolymer of a 3- to 6-functional acrylate-based binder anda 7- to 20-functional urethane acrylate-based binder; and inorganic fineparticles having a bimodal particle size distribution including a firstinorganic fine particle group having d₅₀ of 20 to 35 nm and a secondinorganic fine particle group having d₅₀ of 40 to 130 nm.
 6. Theflexible plastic film according to claim 5, wherein the weight ratiobetween the 3- to 6-functional acrylate-based binder and the 7- to20-functional urethane acrylate-based binder is 1:9 to 4:6.
 7. Theflexible plastic film according to claim 5, wherein the ultravioletcurable coating layer includes the 3- to 6-functional acrylate-basedhinder in an amount of 10 to 50 parts by weight, the 7- to 20-functionalurethane acrylate-based binder in an amount of 40 to 70 parts by weight,the first inorganic fine particle group in an amount of 5 to 50 parts byweight and the second inorganic fine particle group in an amount of 5 to50 parts by weight, based on 100 parts by weight of ultraviolet curablecoating layer.
 8. The flexible plastic film according to claim 5,wherein the first inorganic fine particle group and the second inorganicfine particle group are the same or different and each independentlysurface-modified with any one or more silane coupling agents selectedfrom the group consisting of (meth)acrylsilane, methacroxysilane,vinylsiloxane, epoxysilane, and mercaptosilane.
 9. The flexible plasticfilm according to claim 5, wherein the first inorganic fine particlegroup has d₅₀ of 10 to 19 nm and d₉₀ of 25 to 40 nm, and the secondinorganic fine particle group has d₅₀ of 25 to 110 nm and d₉₀ of 60 to150 nm.
 10. The flexible plastic film according to claim 1, wherein theweight ratio between the first inorganic fine particle group and thesecond inorganic fine particle group is 9:1 to 3:7.
 11. The flexibleplastic film according to claim 1, wherein the support substrate is atleast one selected from the group consisting of polyimide (PI),polyimideamide, polyetherimide polyethyleneterephtalate (PET),polyethylenenaphthalate (PEN), polyetheretherketone (PEEK), cyclicolefin polymer (COP), polyacrylate (PAC), polymethylmethacrylate (PMMA),and triacetylcellulose
 12. The flexible plastic film according to claim1, further comprising an antistatic layer or a low refractive indexlayer on the upper surface or the lower surface of the coating layer.13. The flexible plastic film according to claim 1, wherein a crack doesnot occur when wound on a mandrel with a diameter of 4 mm.
 14. Theflexible plastic film according to claim 1, wherein the flexible plasticfilm has a light transmittance of 88.0% or more, and a haze of 1.5% orless.